EP1364708A1 - Kaltstartautoabgasreinigungskatalysator - Google Patents

Kaltstartautoabgasreinigungskatalysator Download PDF

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Publication number
EP1364708A1
EP1364708A1 EP03015025A EP03015025A EP1364708A1 EP 1364708 A1 EP1364708 A1 EP 1364708A1 EP 03015025 A EP03015025 A EP 03015025A EP 03015025 A EP03015025 A EP 03015025A EP 1364708 A1 EP1364708 A1 EP 1364708A1
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Prior art keywords
layer
exhaust gas
zeolite
gas purifying
purifying catalyst
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English (en)
French (fr)
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Shinji Yamamoto
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Nissan Motor Co Ltd
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Nissan Motor Co Ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B01D53/9445—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC]
    • B01D53/945—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC] characterised by a specific catalyst
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B01D53/9445—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC]
    • B01D53/9454—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC] characterised by a specific device
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
    • B01J23/54—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/56—Platinum group metals
    • B01J23/63—Platinum group metals with rare earths or actinides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/50—Catalysts, in general, characterised by their form or physical properties characterised by their shape or configuration
    • B01J35/56—Foraminous structures having flow-through passages or channels, e.g. grids or three-dimensional monoliths
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/024—Multiple impregnation or coating
    • B01J37/0244—Coatings comprising several layers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/024—Multiple impregnation or coating
    • B01J37/0246—Coatings comprising a zeolite
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
    • F01N13/009—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/0807—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
    • F01N3/0814—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents combined with catalytic converters, e.g. NOx absorption/storage reduction catalysts
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/0807—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
    • F01N3/0828—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents characterised by the absorbed or adsorbed substances
    • F01N3/0835—Hydrocarbons
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/24—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by constructional aspects of converting apparatus
    • F01N3/28—Construction of catalytic reactors
    • F01N3/2803—Construction of catalytic reactors characterised by structure, by material or by manufacturing of catalyst support
    • F01N3/2825—Ceramics
    • F01N3/2828—Ceramic multi-channel monoliths, e.g. honeycombs
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2240/00—Combination or association of two or more different exhaust treating devices, or of at least one such device with an auxiliary device, not covered by indexing codes F01N2230/00 or F01N2250/00, one of the devices being
    • F01N2240/18—Combination or association of two or more different exhaust treating devices, or of at least one such device with an auxiliary device, not covered by indexing codes F01N2230/00 or F01N2250/00, one of the devices being an adsorber or absorber
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2250/00—Combinations of different methods of purification
    • F01N2250/12—Combinations of different methods of purification absorption or adsorption, and catalytic conversion
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2330/00—Structure of catalyst support or particle filter
    • F01N2330/06—Ceramic, e.g. monoliths
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2330/00—Structure of catalyst support or particle filter
    • F01N2330/30—Honeycomb supports characterised by their structural details
    • F01N2330/34—Honeycomb supports characterised by their structural details with flow channels of polygonal cross section
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2370/00—Selection of materials for exhaust purification
    • F01N2370/02—Selection of materials for exhaust purification used in catalytic reactors
    • F01N2370/04—Zeolitic material
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2510/00—Surface coverings
    • F01N2510/06—Surface coverings for exhaust purification, e.g. catalytic reaction
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2510/00—Surface coverings
    • F01N2510/06—Surface coverings for exhaust purification, e.g. catalytic reaction
    • F01N2510/063—Surface coverings for exhaust purification, e.g. catalytic reaction zeolites
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/12—Improving ICE efficiencies

Definitions

  • the present invention relates to a catalyst for purifying exhaust gases from an internal combustion engine of an automobile and, more particularly, an exhaust gas purifying catalyst for removing effectively high concentration hydrocarbons exhausted in engine start-up.
  • the three-way catalyst that can perform oxidation of carbon monoxide (CO) and hydrocarbons (HC) and reduction of nitrogen oxides (NOx) simultaneously has been widely employed.
  • HC HC
  • the exhaust gas temperature must be kept at more than 300 °C to make the above three-way catalyst active
  • the three-way catalyst is inactive at the low temperature immediately after the engine start-up. Therefore, if only the three-way catalyst in the prior art is employed, the cold HC is not purified but exhausted as it is.
  • the HC adsorbing catalyst is such a catalyst that adsorbs and holds temporarily the cold HC in the engine start-up during when the three-way catalyst is not activated, and then desorbs HC gradually to purify HC by using the three-way catalyst when the three-way catalyst is activated after the temperature of the exhaust gas is increased.
  • Such HC absorbing catalysts are disclosed in Japanese Laid-Open Patent publications Hei 6-74019 published in 1994, Hei 7-144119 published in 1995, Hei 6-142457 published in 1994, Hei 5-59942 published in 1993, Hei 7-102957 published in 1995, and Hei 11-104462 published in 1999.
  • the zeolite having the optimum pore diameter must be employed.
  • the pore diameter distribution is adjusted by blending the MFI-type zeolite as the main element with the zeolite (e.g., USY type) having another pore diameter.
  • the zeolite e.g., USY type
  • a three-way catalyst contains noble metals such as platinum (Pt), palladium (Pd), rhodium (Rh), etc. mixed in the same layer and another three-way catalyst contains a Rh layer and a Pd layer coated separately, etc. have been proposed for the noble metals in the three-way catalyst.
  • Japanese Laid-Open Patent Publication Hei 2-56247 published in 1990 discloses an exhaust gas purifying catalyst in which a second layer containing noble metals such as Pt, Pd, Rh, etc. as the main component and having the three-way catalytic function is provided on a first layer containing the zeolite as the main component.
  • such three-way catalyst layer prevents the cold HC diffusing into the zeolite layer and thus makes worse the adsorption efficiency of the cold HC.
  • HC adsorbed in the zeolite is quickly desorbed at the thin portion of the zeolite layer with the increase of the exhaust gas temperature and the increase of the exhaust gas flow rate. If desorption of HC is too quick, HC cannot be effectively purified in the overlying three-way catalyst layer.
  • A/F stoichometric air-fuel ratio
  • the exhaust gas purifying catalyst since HC which has been adsorbed into the zeolite layer in the low temperature zone of the exhaust gases immediately after the start of the internal combustion engine is abruptly desorbed with the increase of the exhaust gas temperature, the exhaust gas becomes fuel-rich. Therefore, the three-way catalyst does not fulfill sufficiently the purification function, the purification of HC, Co, NOx is not performed with good balance.
  • the inner wall of the coating layer is formed substantially like an inscribed circle of the polygonal cell.
  • a thickness of the coating layer is thick at the cell corner portion while a thickness of the coating layer is thin at the cell side portion. Therefore, there is such a tendency that the adsorption/desorption characteristic of the zeolite in the cell side portion is considerably degraded rather than that in the cell corner portion.
  • the monolithic supports having the cells whose inner wall sectional shape is a circle is employed.
  • a thickness of the wall portion corresponding to the cell corner portion is increased and thus a volume of the support itself is increased.
  • the purification efficiency of HC desorbed from the zeolite layer is considerably degraded.
  • the catalyst that enables the high performance by the reduced amount of the noble metal is desired.
  • the durability of the catalyst becomes insufficient and thus the catalytic activity and the purification performance are deteriorated in the low temperature zone after the endurance time.
  • an object of the present invention to provide an exhaust gas purifying catalyst capable of achieving purification of HC, CO, and NOx with good balance and improving the purification performance of cold HC by controlling the diffusion (speed) of the exhaust gases that pass through cells in a support and diffuse into coating layers.
  • such exhaust gas purifying catalyst comprises a monolithic support having a plurality of cells each of which has a polygonal sectional shape, a first layer formed on a monolithic support to contain heat resisting inorganic material, a second layer formed on the first layer to contain hydrocarbon adsorbent, and a third layer formed on the second layer to contain a metal-based catalyst.
  • the second layer has a ratio Lmax/Lmin of the thickest portion (Lmax) at corner portions of the cells to the thinnest portion (Lmin) at flat portions of the cells in a range of 1 to 10
  • the second layer has a thickness of 10 to 500 ⁇ m.
  • ceramic materials such as alumina, titania, zirconia, etc. may be listed.
  • the second layer containing hydrocarbon adsorbent as the main component (called the hydrocarbon adsorbent layer hereinafter) is not directly formed on the monolithic support but formed on the first layer containing the heat resisting inorganic material as the main component.
  • the first layer thickly covers the cell corner portions of the support, and brings inner walls of the cells close to the circular shape. Therefore, the thickness of the hydrocarbon adsorbent layer can be adjusted into the appropriate range.
  • HC adsorption/desorption/purification cycles are carried out effectively, and such HC adsorption/ desorption/purification can be performed uniformly over the entire second layer without deviation.
  • a catalytic component layer containing Pd may be employed as the third layer and then an insoluble salt of an alkaline earth metal may be contained in this layer. Sintering of the noble metal can be suppressed and thus the low temperature activity and the purification performance can be improved.
  • the cold HC adsorbing/desorbing ability characteristic and the desorbed HC purification performance can be effectively exhibited.
  • platinum (Pt) may be mixed in the third layer and the fourth layer. Therefore, the poisoning resistance of the third layer as the catalytic component layer (three-way catalyst layer) can be improved.
  • FIG. 1 shows a configuration of an exhaust gas purifying catalyst according to the present embodiment.
  • An outer perspective view of the exhaust gas purifying catalyst is illustrated on the upper side of FIG. 1, and an enlarged sectional view of a part of the exhaust gas purifying catalyst corresponding to a single cell is illustrated on the lower side of FIG. 1.
  • a first layer 2 containing heat resisting inorganic material, a second layer 3 containing hydrocarbon adsorbing material, and a third layer 4 containing the metal catalyst are laminated sequentially on a monolithic support 1 that has a plurality of cells whose sectional shape is a polygon.
  • the exhaust gases flow through the center area of the cell on the inside of the third layer 4.
  • a sectional shape of the cell may be regular quadrangle, regular triangle or regular hexagonal as shown in FIGs 1, 2A and 2B. Also the shape of the cell may be slightly deformed.
  • the first layer 2 containing heat resisting inorganic material covers thickly respective corner portions of the cell of the monolithic support 1 to form the inner wall sectional shape of the cell substantially into a circular shape. Therefore, in the exhaust gas purifying catalyst according to the present embodiment, difference in the film thickness of the hydrocarbon adsorbent layer (referred to as an "HC adsorbent layer” hereinafter) as the second layer 3 laminated on the first layer 2 can be reduced between the cell corner portion 5 and the cell side (flat) portion and thus the uniform layer can be easily formed on the overall inner wall of the cell.
  • HC adsorbent layer hydrocarbon adsorbent layer
  • the ratio Lmax/Lmin of the thickest portion to the thinnest portion exceeds 10, desorption of HC at the thinnest portion becomes too quick and therefore the purification efficiency of HC being desorbed from the HC adsorbent layer 3 is degraded. Also, if the thickness of the HC adsorbent layer 3 is less than 10 ⁇ m, the HC adsorbing ability and the desorption suppressing effect cannot be sufficiently obtained. In contrast, if the thickness of the HC adsorbent layer 3 exceeds 500 ⁇ m, the HC adsorbing ability and the desorption suppressing effect are saturated. Therefore, improvement of the cold HC adsorption efficiency and the HC desorption suppression can be attained by setting the thickness of the HC adsorbent layer 3 within the above range.
  • the heat resisting inorganic material interposed between the monolithic support 1 and the HC adsorbent layer (second layer) 3 can improve adhesiveness of the HC adsorbent layer 3, and also has an effect of preventing the peeling of the HC adsorbent layer 3 from the monolithic support 1.
  • the third layer 4 formed on the HC adsorbent layer 3 to contain the metal catalyst (referred to as a "metal-based catalyst layer” hereinafter) can purify effectively HC desorbed from the HC adsorbent layer 3. If Pd that is excellent in the activating operation for the HC oxidation reaction is used as the metal catalyst, the purification of HC, CO, and NOx can be performed with good balance even when the inside of the metal-based catalyst layer 4 becomes fuel-rich atmosphere.
  • the HC adsorbent layer 3 Since the HC adsorbent layer 3 is formed under the metal-based catalyst layer 4, such HC adsorbent layer 3 does not directly come into contact with the exhaust gases passing through the cell. Therefore, the increase of the temperature of the HC adsorbent layer 3 is delayed in contrast to the metal-based catalyst layer 4, so that the HC adsorbent layer holds the adsorbed HC longer. On the contrary, since the metal-based catalyst layer 4 directly comes into contact with the exhaust gases passing through the cell to increase its temperature quickly, the three-way catalyst is quickly activated. As a result, balance of HC adsorption/desorption/purification becomes good.
  • the heat resisting inorganic material used in the first layer 2 for example, various ceramic materials such as alumina (Al 2 O 3 ), titania (TiO 2 ), zirconia (ZrO 2 ), etc. may be listed.
  • alumina Al 2 O 3
  • titania TiO 2
  • zirconia zirconia
  • the alumina having a large specific surface area and a large bulk should be employed, although not particularly limited.
  • the alumina such as ⁇ -alumina is desired.
  • the HC adsorbent layer used in the second layer 3 various zeolites may be listed. If the H-type ⁇ -zeolite whose Si/2Al ratio is at least 10 to 1500 is used as the main component of the zeolite, the wide adsorbing ability for various HCs having different molecular diameters in the exhaust gases can be exhibited, and also destruction of the zeolite structure under the high temperature and the moisture existing atmosphere can be suppressed. Therefore, the HC adsorbent layer can get the high adsorbing ability from the beginning to the endurance time.
  • the Si/2Al ratio of the H-type ⁇ -zeolite is less than 10, the heat resistance is low and in some times the sufficient adsorbing ability cannot be attained after the endurance time. In contrast, if the Si/2Al ratio exceeds 1500, the heat resistance improving effect cannot be achieved and inversely desorption of HC from the H-type ⁇ -zeolite is accelerated considerably. In some cases, the postprocessing effect of the desorbed HC becomes worse.
  • the HC adsorbent layer can exhibit the wider adsorbing ability for various HCs having different molecular diameters in the exhaust gases.
  • an amount of the MFI-type zeolite, etc. added to the H-type ⁇ -zeolite should be set to 10 weight % to 50 weight % of the total zeolite amount.
  • any one of palladium (Pd), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), silver (Ag), yttrium (Y), lanthanum (La), cerium (Ce), neodymium (Nd), phosphorus (P), boron (B), and zirconium (Zr), or two or more of them may be contained in the zeolite type of the above second layer. Accordingly, since the HC holding force of the zeolite can be improved, desorption of a variety of HCs having different molecular diameters in the exhaust gases can be delayed. Also, the heat resistance and the structural stability can be improved.
  • a contained amount of such Pd. Mg, Ca, etc. should be set to 0.1 weight % to 10 weight %. If such contained amount is less than 0.1 weight %, suppressing desorption effect of the added elements for cannot be sufficiently exhibited whereas, if such contained amount exceeds 10 weight %, the adsorbing ability becomes worse because the pores of the zeolite are blocked.
  • the zirconium oxide that contains any one or two or more of Ce, Nd, and La and Rh by 1 to 40 mol % in terms of metal may be contained in the HC adsorbent layer 3 containing the H-type ⁇ -zeolite as the main component. Therefore, the purification efficiency of HC desorbed from the zeolite can be improved.
  • an amount of Rh contained in the HC adsorbent layer 3 should be set to 0.001 g/L to 1 g/L.
  • An action for improving the desorbed HC purification efficiency by Rh cannot be enoughly attained if such amount is less than 0.001 g/L, but such action for improving the desorbed HC purification efficiency by Rh is saturated if the amount is in excess of 1 g/L.
  • the contained amount of the zirconium oxide in the HC adsorbent layer 3 should be set to 1 g/L to 50 g/L.
  • the degradation suppressing action of Rh by adding the zirconium oxide cannot be satisfactorily obtained if such contained amount is less than, whereas the adding effect is saturated if contained amount is in excess of 50 g/L.
  • Pd, Pt, Rh, or the like may be thought of as the catalytic component used in the metal-based catalyst layer 4.
  • Various elements having the so-called three-way catalytic function may be employed.
  • Pd is preferable, for Pd is excellent in the activating action of the HC oxidation reaction and thus Pd can perform the purification of HC, CO, and NOx with good balance even when the inside of the metal-based catalyst layer 4 becomes fuel-rich atmosphere.
  • the insoluble alkaline earth metal salt e.g., insoluble barium salt should be added.
  • the added alkaline earth metal, etc. suppresses the sintering of Pd and sustains the purification characteristic.
  • the added alkaline earth metal, etc. alleviate HC poisoning Pd.
  • the contained amount of the alkaline earth metal should be set to 1 g/L to 30 g/L in terms of oxide. If the oxide amount of the alkaline earth metal element is less than 1 g/L, the alleviating HC poisoning effect is small and thus the low temperature activation improving effect cannot be sufficiently achieved. In contrast, if the oxide amount of the alkaline earth metal element exceeds 30 g/L, the HC adsorbing ability of Pd is remarkably reduced and inversely the low temperature activity is degraded.
  • the fourth layer containing Rh may be laminated on the third layer.
  • the poisoning Pd in the third layer due to P, Pb (lead), etc. in the exhaust gases can be suppressed.
  • the exhaust gas purifying catalyst of the present embodiment may have such a structure that Pd having an excellent HC oxidation activity is used as the catalytic component of the metal-based catalyst layer (third layer) 4 and then either Rh is also contained in the same layer or an Rh layer is provided thereon as the fourth layer.
  • Pd having an excellent HC oxidation activity is used as the catalytic component of the metal-based catalyst layer (third layer) 4 and then either Rh is also contained in the same layer or an Rh layer is provided thereon as the fourth layer.
  • the above noble metal is contained in the metal-based catalyst layer (third layer) 4 but materials other than these noble metals may be added.
  • the alumina containing any one of Ce, Zr, and La or two or more of them by 1 to 10 mol % in terms of metal and the cerium oxide containing any one of Zr, Nd, and La or two or more of them by 1 to 40 mol % in terms of metal may be contained. In such case, degradation of Pd in the oxygen deficient atmosphere can be suppressed.
  • an amount of the cerium oxide contained in the metal-based catalyst layer (third layer) 4 should be set to 1 g/L to 200 g/L.
  • the Pd degradation suppressing effect obtained by adding the cerium oxide cannot be satisfactorily attained if such amount is less than 1 g/L, whereas the adding effect is saturated if such amount is in excess of 200 g/L.
  • the zirconium oxide that contains any one or two or more of Ce, Zr, and La or two or more of them by 1 to 40 mol % in terms of metal is contained other than the above cerium oxide, degradation of Pd in the oxygen deficient atmosphere can be suppressed.
  • an amount of the zirconium oxide contained in the third layer should be set to 1 g/L to 200 g/L.
  • the Rh degradation suppressing effect obtained by adding the zirconiums oxide cannot be satisfactorily attained if such amount is less than 1 g/L, whereas the adding effect is saturated if such amount is in excess of 200 g/L.
  • the monolithic support employed in the exhaust gas purifying catalyst ceramic or metal monolithic support can be considered.
  • the cell sectional shape of this support should be formed as a polygon such as a triangle, a quadrilateral, a hexagon, an octagon, etc., and more preferably the cell sectional shape should be formed as a regular polygon.
  • the HC adsorbent layer (second layer) 3 and the metal-based catalyst layer (third layer) 4 are impregnated in the support whose cell number is 100 to 1000 1/L. Desorption of HC from the zeolite layer can be delayed. As the exhaust gases contact the three-way catalytic component layer sufficiently, the exhaust gases are purified well.
  • the slurry solution is prepared by introducing ⁇ -alumina of 400 g, nitric acid alumina sol (sol obtained by adding 10 weight % nitric acid into 10 weight % boehmite alumina) of 1000 g, and a pure water of 500 g into a magnetic ball mill, and then crushing the mixture.
  • This slurry solution is coated on the cordierite monolithic support (1.3 L) whose cell density is 600 cells/4 mil.
  • the excessive slurry in the cells is removed by an air flow, then dried, and then burned at 400 °C for one hour.
  • An alumina layer A acting as the first layer is obtained by repeating the coating operation after the burning until the coated amount of the slurry comes up to 100 g/L.
  • This slurry solution is coated on the alumina layer 1A.
  • the excessive slurry in the cells is removed by an air flow, then dried, and then burned at 400 °C for one hour.
  • a catalyst layer B acting as the HC adsorbent layer of the second layer is obtained by repeating the coating operation until the coated amount of the slurry after the burning comes up to 150 g/L.
  • the Pd-impregnated alumina powder (powder I) is prepared by impregnating the alumina powder containing 3 mol % Ce with a palladium nitrate aqueous solution, then drying the resultant at 150 °C for twenty four hours, and then burning the resultant at 400 °C for one hour and then at 600 °C for one hour.
  • a Pd concentration in this powder I is 8.0 weight %. In this case, lanthanum, zirconium, neodymium, etc. may be contained into the powder I.
  • the Pd-impregnated cerium oxide powder (powder II) is prepared by impregnating the cerium oxide powder containing 1 mol % La and 32 mol % Zr with the palladium dinitrodiamine aqueous solution, then drying the resultant at 150 °C for twenty four hours, and then burning the resultant at 400 °C for one hour and then at 600 °C for one hour.
  • a Pd concentration in this powder II is 4.0 weight %.
  • Lanthanum, neodymium, etc. may be contained into the cerium oxide powder.
  • the slurry solution is prepared by introducing the Pd-impregnated alumina powder (powder I) of 400 g, the Pd-impregnated cerium oxide powder (powder II) of 141 g, the barium carbonate powder of 64 g, the nitric acid alumina sol of 8.5 g (sol obtained by adding 10 weight % nitric acid into 10 weight % boehmite alumina), and the pure water of 1000 g into a magnetic ball mill, and then crushing the mixture. Then, this slurry solution is coated on the catalyst layer B. Then, the excessive slurry in the cells is removed by the air flow, and then the slurry is dried and then burned at 400 °C for one hour. Thus, a catalyst layer C acting as the metal-based catalyst layer of the third layer is formed repeating the coating operation until the coated amount of the slurry after the burning comes up to 60 g/L.
  • the Rh-impregnated alumina powder (powder III) is prepared by impregnating the alumina powder containing 3 weight % Zr with the rhodium nitrate aqueous solution, then drying the resultant at 150 °C for twenty four hours, and then burning the resultant at 400 °C for one hour and then at 600 °C for one hour.
  • a Rh concentration in this powder III is 5.0 weight %.
  • the Pt-impregnated alumina powder (powder IV) is prepared by impregnating the alumina powder containing 3 weight % Ce with the platinum dinitrodiamine aqueous solution, then drying the resultant at 150 °C for twenty four hours, and then burning the resultant at 400 °C for one hour and then at 600 'C for one hour.
  • a Pt concentration in this powder IV is 5.0 weight %.
  • the slurry solution is prepared by introducing the Rh-impregnated alumina powder (powder III) of 283g, Pt-impregnated alumina powder (powder IV) of 94g, the zirconium oxide powder of 100 g containing 1 mol % La and 20 mol % Ce, and the nitric acid alumina sol of 23 g into the magnetic ball mill, and then crushing the mixture. Then, this slurry solution is coated on the above catalyst layer C. Then, the excessive slurry in the cells is removed by the air flow, and then the slurry is dried and then burned at 400 °C for one hour. Thus, a catalyst layer D acting as the rhodium containing layer of the fourth layer is formed repeating the coating operation until a weight of the coated layer after the burning comes up to 50 g/L (total coated amount is 360 g/L).
  • An average of the maximum thicknesses Lmax at the cell corner portions of the HC adsorbent layer (second layer) in EXAMPLE #1 is 85 ⁇ m, and an average of the minimum thicknesses Lmin at the cell flat portions is 20 ⁇ m.
  • the ratio Lmax/Lmin is 4.3.
  • the exhaust gas purifying catalyst is prepared under the same conditions as EXAMPLE #1 except for the above.
  • An average of the maximum thicknesses Lmax at the cell corner portions of the HC adsorbent layer (second layer) in EXAMPLE #2 is 90 ⁇ m, and an average of the minimum thicknesses Lmin at the cell flat portions is 15 ⁇ m.
  • the ratio Lmax/Lmin is 6.0.
  • the exhaust gas purifying catalyst is prepared under the same conditions as EXAMPLE #1 except for the above.
  • An average of the maximum thicknesses Lmax at the cell corner portions of the HC adsorbent layer (second layer) in EXAMPLE #3 is 80 ⁇ m, and an average of the minimum thicknesses Lmin at the cell flat portions is 30 ⁇ m.
  • the ratio Lmax/Lmin is 2.7.
  • the exhaust gas purifying catalyst is prepared under the same conditions as EXAMPLE #1 except for the above.
  • An average of the maximum thicknesses Lmax at the cell corner portions of the HC adsorbent layer (second layer) in EXAMPLE #4 is 80 ⁇ m, and an average of the minimum thicknesses Lmin at the cell flat portions is 25 ⁇ m.
  • the ratio Lmax/Lmin is 3.2.
  • the metal-based catalyst layer (third layer) the slurry prepared by mixing all the powder I, the powder II, the powder III, the powder IV, the barium carbonate, and the nitrid acid alumina sol is used. That is, components of the fourth layer are mixed into the third layer.
  • the exhaust gas purifying catalyst is prepared under the same conditions as EXAMPLE #1 except for the above.
  • An average of the maximum thicknesses Lmax at the cell corner portions of the HC adsorbent layer (second layer) in EXAMPLE #5 is 80 ⁇ m, and an average of the minimum thicknesses Lmin at the cell flat portions is 25 ⁇ m.
  • the ratio Lmax/Lmin is 3.2.
  • An average of the maximum thicknesses Lmax at the cell corner portions of the HC adsorbent layer (second layer) in EXAMPLE #6 is 85 ⁇ m, and an average of the minimum thicknesses Lmin at the cell flat portions is 25 ⁇ m.
  • the ratio Lmax/Lmin is 3.4.
  • mordenite powder of 50 g are used.
  • the exhaust gas purifying catalyst is prepared under the same conditions as EXAMPLE #1 except for the above.
  • An average of the maximum thicknesses Lmax at the cell corner portions of the HC adsorbent layer (second layer) in EXAMPLE #7 is 85 ⁇ m, and an average of the minimum thicknesses Lmin at the cell flat portions is 25 ⁇ m.
  • the ratio Lmax/Lmin is 3.4.
  • the exhaust gas purifying catalyst is prepared under the same conditions as EXAMPLE #1 except for the above.
  • An average of the maximum thicknesses Lmax at the cell corner portions of the HC adsorbent layer (second layer) in EXAMPLE #8 is 90 ⁇ m, and an average of the minimum thicknesses Lmin at the cell flat portions is 20 ⁇ m.
  • the ratio Lmax/Lmin is 4.5.
  • the powder of 10 g obtained by impregnating the '3-zeolite powder (H type, Si/2Al 75) with 0.01 weight % Mg, 0.01 weight % Ce, and 0.01 weight % Zr
  • the powder of 10 g obtained by impregnating the MFI powder with 0.01 weight % Ca, 0.01 weight % Y, and 0.01 weight % B the powder of 10 g obtained by impregnating the mordenite powder with 0.2 weight % Pd
  • the powder of 10 g obtained by impregnating the Y-zeolite powder with 0.01 weight % Sr and 0.01 weight % La and
  • An average of the maximum thicknesses Lmax at the cell corner portions of the HC adsorbent layer (second layer) in EXAMPLE #9 is 90 ⁇ m, and an average of the minimum thicknesses Lmin at the cell flat portions is 25 ⁇ m.
  • the ratio Lmax/Lmin is 3.6.
  • the exhaust gas purifying catalyst is prepared under the same conditions as EXAMPLE #1 except for the employment of the support whose cell density is 900 cells/2 mil as the monolithic support.
  • An average of the maximum thicknesses Lmax at the cell corner portions of the HC adsorbent layer (second layer) in EXAMPLE #10 is 70 ⁇ m, and an average of the minimum thicknesses Lmin at the cell flat portions is 12 ⁇ m.
  • the ratio Lmax/Lmin is 5.8.
  • the coated amount of the alumina layer as the first alyer is set to 150 g/L, and the coated amount of the ⁇ -zeolite component layer in the HC adsorbent layer as the second layer is set to 100 g/L.
  • the exhaust gas purifying catalyst is prepared under the same conditions as EXAMPLE #1 except for the above.
  • An average of the maximum thicknesses Lmax at the/cell corner portions of the HC adsorbent layer (second layer) in EXAMPLE #11 is 55 ⁇ m, and an average of the minimum thicknesses Lmin at the cell flat portions is 20 ⁇ m.
  • the ratio Lmax/Lmin is 2.8.
  • the coated amount of the alumina layer as the first layer is set to 50 g/L, and the coated amount of the ⁇ -zeolite component layer in the HC adsorbent layer as the second layer is set to 150 g/L.
  • the exhaust gas purifying catalyst is prepared under the same conditions as EXAMPLE #1 except for the above.
  • An average of the maximum thicknesses Lmax at the cell corner portions of the HC adsorbent layer (second layer) in EXAMPLE #12 is 100 ⁇ m, and an average of the minimum thicknesses Lmin at the cell flat portions is 12 ⁇ m.
  • the ratio Lmax/Lmin is 8.3.
  • the coated amount of the alumina layer as the first layer is set to 50 g/L, and the coated amount of the ⁇ -zeolite component layer in the HC adsorbent layer as the second layer is set to 250 g/L.
  • the exhaust gas purifying catalyst is prepared under the same conditions as EXAMPLE #1 except for the above.
  • An average of the maximum thicknesses Lmax at the cell corner portions of the HC adsorbent layer (second layer) in EXAMPLE #13 is 130 ⁇ m, and an average of the minimum thicknesses Lmin at the cell flat portions is 20 ⁇ m.
  • the ratio Lmax/Lmin is 6.5.
  • the metal support whose cell sectional shape is a triangle and whose cell density is 200 cells/30 ⁇ m is used as the monolithic support.
  • the coated amount of the alumina layer as the first layer is set to 150 g/L
  • the coated amount of the ⁇ -zeolite component layer in the HC adsorbent layer as the second layer is set to 150 g/L.
  • the exhaust gas purifying catalyst is prepared under the same conditions as EXAMPLE #1 except for the above.
  • An average of the maximum thicknesses Lmax at the cell corner portions of the HC adsorbent layer (second layer) in EXAMPLE #14 is 650 ⁇ m, and an average of the minimum thicknesses Lmin at the cell flat portions is 160 ⁇ m.
  • the ratio Lmax/Lmin is 4.1.
  • the support whose cell density is 200 cells/10 mil is used as the monolithic support.
  • the coated amount of the alumina layer as the first layer is set to 100 g/L, and the coated amount of the ⁇ -zeolite component layer in the HC adsorbent layer as the second layer is set to 250 g/L.
  • the exhaust gas purifying catalyst is prepared under the same conditions as EXAMPLE #1 except for the above.
  • An average of the maximum thicknesses Lmax at the cell corner portions of the HC adsorbent layer (second layer) in EXAMPLE #15 is 300 ⁇ m, and an average of the minimum thicknesses Lmin at the cell flat portions is 280 ⁇ m.
  • the ratio Lmax/Lmin is 1.1.
  • the support whose cell density is 200 cells/10 mil is used as the monolithic support.
  • the coated amount of the alumina layer as the first layer is set to 100 g/L, and the coated amount of the ⁇ -zeolite component layer in the HC adsorbent layer as the second layer is set to 150 g/L.
  • the exhaust gas purifying catalyst is prepared under the same conditions as EXAMPLE #1 except for the above.
  • An average of the maximum thicknesses Lmax at the cell corner portions of the HC adsorbent layer (second layer) in EXAMPLE #16 is 230 ⁇ m, and an average of the minimum thicknesses Lmin at the cell flat portions is 150 ⁇ m.
  • the ratio Lmax/Lmin is 1.5.
  • the support whose cell density is 300 cells/6 mil is used as the monolithic support.
  • the coated amount of the alumina layer as the first layer is set to 100 g/L, and the coated amount of the ⁇ -zeolite component layer in the HC adsorbent layer as the second layer is set to 150 g/L.
  • the exhaust gas purifying catalyst is prepared under the same conditions as EXAMPLE #1 except for the above.
  • An average of the maximum thicknesses Lmax at the cell corner portions of the HC adsorbent layer (second layer) in EXAMPLE #17 is 200 ⁇ m, and an average of the minimum thicknesses Lmin at the cell flat portions is 120 ⁇ m.
  • the ratio Lmax/Lmin is 1.7.
  • the barium acetate aqueous solution is used in place of the barium carbonate.
  • the exhaust gas purifying catalyst is prepared under the same conditions as EXAMPLE #1 except for the above.
  • An average of the maximum thicknesses Lmax at the cell corner portions of the HC adsorbent layer (second layer) in EXAMPLE #18 is 80 ⁇ m, and an average of the minimum thicknesses Lmin at the cell flat portions is 15 ⁇ m.
  • the ratio Lmax/Lmin is 5.3.
  • a titania layer is formed on the monolithic support, in place of the alumina layer.
  • the exhaust gas purifying catalyst is prepared under the same conditions as EXAMPLE #1 except for the above.
  • An average of the maximum thicknesses Lmax at the cell corner portions of the HC adsorbent layer (second layer) in EXAMPLE #19 is 85 ⁇ m, and an average of the minimum thicknesses Lmin at the cell flat portions is 22 ⁇ m.
  • the ratio Lmax/Lmin is 3.9.
  • a zirconia layer is formed on the monolithic support, in place of the alumina layer.
  • the exhaust gas purifying catalyst is prepared under the same conditions as EXAMPLE #1 except for the above.
  • An average of the maximum thicknesses Lmax at the cell corner portions of the HC adsorbent layer (second layer) in EXAMPLE #20 is 80 ⁇ m, and an average of the minimum thicknesses Lmin at the cell flat portions is 20 ⁇ m.
  • the ratio Lmax/Lmin is 4.0.
  • the cordierite monolithic support whose cell sectional shape is an almost regular hexagon is used as the support for the exhaust gas purifying catalyst.
  • the cell density of this support is 300 cells/3.5 mil.
  • the exhaust gas purifying catalyst is prepared under the same conditions as EXAMPLE #1 except for the above.
  • An average of the maximum thicknesses Lmax at the cell corner portions of the HC adsorbent layer (second layer) in EXAMPLE #21 is 70 ⁇ m, and an average of the minimum thicknesses Lmin at the cell flat portions is 50 ⁇ m.
  • the ratio Lmax/Lmin is 1.4.
  • the components in the third layer are exchanged with those in the fourth layer. That is, the third layer is formed of the layer containing Rh as the main component and the fourth layer is formed of the layer containing Pd as the main component.
  • the exhaust gas purifying catalyst is prepared under the same conditions as EXAMPLE #1 except for the above.
  • An average of the maximum thicknesses Lmax at the cell corner portions of the HC adsorbent layer (second layer) in EXAMPLE #22 is 80 ⁇ m, and an average of the minimum thicknesses Lmin at the cell flat portions is 25 ⁇ m.
  • the ratio Lmax/Lmin is 3.4.
  • the cerium oxide is not contained in the third layer, and the zirconium oxide is not contained in the fourth layer.
  • the exhaust gas purifying catalyst is prepared under the same conditions as EXAMPLE #1 except for the above.
  • An average of the maximum thicknesses Lmax at the cell corner portions of the HC adsorbent layer (second layer) in EXAMPLE #23 is 80 ⁇ m, and an average of the minimum thicknesses Lmin at the cell flat portions is 20 ⁇ m.
  • the ratio Lmax/Lmin is 4.0.
  • the barium carbonate is not contained in the third layer.
  • the exhaust gas purifying catalyst is prepared under the same conditions as EXAMPLE #1 except for the above.
  • An average of the maximum thicknesses Lmax at the cell corner portions of the HC adsorbent layer (second layer) in EXAMPLE #24 is 80 ⁇ m, and an average of the minimum thicknesses Lmin at the cell flat portions is 20 ⁇ m.
  • the ratio Lmax/Lmin is 4.0.
  • the barium carbonate of 643 g is added into the slurry used to manufacture the third layer.
  • the exhaust gas purifying catalyst is prepared under the same conditions as EXAMPLE #1 except for the above.
  • An average of the maximum thicknesses Lmax at the cell corner portions of the HC adsorbent layer (second layer) in EXAMPLE #25 is 80 ⁇ m, and an average of the minimum thicknesses Lmin at the cell flat portions is 20 ⁇ m.
  • the ratio Lmax/Lmin is 4.0.
  • the ⁇ -zeolite of 50 g and the MFI of 350 g are used.
  • the exhaust gas purifying catalyst is prepared under the same conditions as EXAMPLE #1 except for the above.
  • An average of the maximum thicknesses Lmax at the cell corner portions of the HC adsorbent layer (second layer) in EXAMPLE #26 is 75 ⁇ m, and an average of the minimum thicknesses Lmin at the cell flat portions is 25 ⁇ m.
  • the ratio Lmax/Lmin is 3.0.
  • the Y-type zeolite of 400 g is used as the zeolite added into the slurry solution for the HC adsorbent layer.
  • the exhaust gas purifying catalyst is prepared under the same conditions as EXAMPLE #1 except for the above.
  • An average of the maximum thicknesses Lmax at the cell corner portions of the HC adsorbent layer (second layer) in EXAMPLE #27 is 75 ⁇ m, and an average of the minimum thicknesses Lmin at the cell flat portions is 20 ⁇ m.
  • the ratio Lmax/Lmin is 3.8.
  • the ⁇ -zeolite being impregnated with 30 weight % Ag and 5 weight % P is used instead of the ⁇ -zeolite.
  • the exhaust gas purifying catalyst is prepared under the same conditions as EXAMPLE #1 except for the above.
  • An average of the maximum thicknesses Lmax at the cell corner portions of the HC adsorbent layer (second layer) in EXAMPLE #28 is 75 ⁇ m, and an average of the minimum thicknesses Lmin at the cell flat portions is 20 ⁇ m.
  • the ratio Lmax/Lmin is 3.8.
  • the alumina component layer as the first layer is not formed, and the HC adsorbent layer is coated directly on the monolithic support.
  • the exhaust gas purifying catalyst is prepared under the same conditions as EXAMPLE #1 except for the above.
  • An average of the maximum thicknesses Lmax at the cell corner portions of the HC adsorbent layer (second layer) in COMPARATIVE EXAMPLE #1 is 110 ⁇ m, and an average of the minimum thicknesses Lmin at the cell flat portions is 10 ⁇ m.
  • the ratio Lmax/Lmin is 11.0.
  • the alumina component layer as the first layer is not formed, and the HC adsorbent layer is coated directly on the monolithic support.
  • the exhaust gas purifying catalyst is prepared under the same conditions as EXAMPLE #15 except for the above.
  • An average of the maximum thicknesses Lmax at the cell corner portions of the HC adsorbent layer (second layer) in COMPARATIVE EXAMPLE #2 is 400 ⁇ m, and an average of the minimum thicknesses Lmin at the cell flat portions is 150 ⁇ m.
  • the ratio Lmax/Lmin is 2.7.
  • the alumina component layer as the first layer is not formed, and the HC adsorbent layer is coated directly on the monolithic support.
  • the coated amount of the ⁇ -zeolite component layer of the HC adsorbent layer is set to 250 g/L.
  • the exhaust gas purifying catalyst is prepared under the same conditions as EXAMPLE #14 except for the above.
  • An average of the maximum thicknesses Lmax at the cell corner portions of the HC adsorbent layer (second layer) in COMPARATIVE EXAMPLE #3 is 770 ⁇ m, and an average of the minimum thicknesses Lmin at the cell flat portions is 40 ⁇ m.
  • the ratio Lmax/Lmin is 19.3.
  • FIG.3 shows an arrangement of catalysts employed to evaluate the performance of the exhaust gas purifying catalyst according to the present embodiment.
  • the normal three-way catalyst 20 is arranged on the downstream side of the exhaust gas from the engine 30, and then the exhaust gas purifying catalyst 10 of the present embodiment is arranged on the downstream side of the three-way catalyst 20.
  • the alumina layer (first layer) is provided on the monolithic support
  • the zeolite layer (second layer) as the HC adsorbent layer is provided on the alumina layer
  • the thickness of the zeolite layer is adjusted in a range of 10 to 650 ⁇ m such that a ratio Lmax/Lmin of the thickest portion (Lmax) of the zeolite layer at cell corner portions to the thinnest portion (Lmin) at cell flat portions is within a range of 1 to 10.
  • the presence of the alumina layer has effects of reducing the Lmax/Lmin of the zeolite layer and uniformizing the thickness of the zeolite layer. This is because the alumina layer covers the cell corner portions thickly and brings the cell inner wall sectional shape close to the circular shape. In other words, the presence of the alumina layer can give such a structure that the thickness of the zeolite layer is more easily adjusted to proper ranges of 10 ⁇ m to 650 ⁇ m and the ratio of Lmax/Lmin is adjusted 1 to 10.
  • the zeolite layer whose thickness is adjusted to a proper thickness can control the diffusion (speed) of the exhaust gases that are passed through the cell and diffused into the metal-based catalyst layer and the HC adsorbent layer, and thus improve the cold HC purification performance.
  • the ratio Lmax/Lmin of the zeolite layer should be set to 1 to 5 and also the thickness of the zeolite layer should be set to 50 ⁇ m to 300 ⁇ m.
  • the catalysts prepared by EXAMPLES in which the ⁇ -zeolite having two type pore diameters and having the excellent durability is used as the main component of the HC adsorbent layer can have smaller distortion after the endurance time and can hold the wide pore distribution from the beginning to the end of the endurance time. Therefore, it can be understood that the adsorption/desorption characteristic can be improved rather than the prior art.
  • either the Pd and Rh coexisting layer is provided on the HC adsorbent layer or the Pd layer is provided on the zeolite layer and then the Rh layer is provided thereon, and then Pt is added in either one layer or both layers.
  • Rh is also contained in the Pd layer or the Rh layer is provided on the Pd layer, HC, CO, and NOx in the exhaust gases that are shifted to the atmosphere being slightly fuel-richer than the stoichometric air-fuel ratio can be purified with good balance. As a result, the good conversion rate can be provided.
  • EXAMPLE #1 As can be seen from the comparison between EXAMPLE #1 and EXAMPLE #24, if an appropriate amount of the alkaline earth metal such as the barium carbonate, etc. is contained in the metal-based catalyst layer, sintering of the noble metal can be suppressed. Therefore, the low temperature activity and the purification performance can be improved further more.
  • the alkaline earth metal such as the barium carbonate, etc.
  • the desorbed cold HC can be purified effectively by the action of suppressing the degradation of Pd in the oxygen deficient atmosphere.
  • the poisoning resistance in the exhaust gases can be improved by adding Pt into the fourth layer.

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EP1843017A1 (de) * 2006-04-03 2007-10-10 HONDA MOTOR CO., Ltd. Abgasreinigungsvorrichtung
US7473665B2 (en) 2003-03-20 2009-01-06 Cataler Corporation Exhaust gas-purifying catalyst system
US7767164B2 (en) 2006-04-03 2010-08-03 Honda Motor Co., Ltd. Catalytic converter apparatus for purifying exhaust gas
WO2011121562A1 (en) * 2010-04-01 2011-10-06 Basf Se Process for the preparation of coated monoliths
CN109590021A (zh) * 2018-11-23 2019-04-09 中汽研（天津）汽车工程研究院有限公司 一种夹心结构的氨泄漏催化剂及其制备方法和应用

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JP3664019B2 (ja) * 1999-12-27 2005-06-22 日産自動車株式会社 触媒コンバータ
JP3797081B2 (ja) * 2000-09-08 2006-07-12 トヨタ自動車株式会社 吸収還元型ＮＯｘ浄化用触媒
JP4863596B2 (ja) 2001-06-18 2012-01-25 日産自動車株式会社 排気ガス浄化システム
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